I'm having trouble understanding the difference between a biserial correlation coefficient and a tetrachoric correlation coefficient.

Could someone please provide an example of each to help me understand the difference?

Thanks!!

From Google:

Biserial and Polychoric. You know that the point biserial correlation coefficient is used to measure the association between a dichotomous variable and a continuous variable. ... When both variables are dichotomous the polychoric correlation coefficient may be called the tetrachoric correlation coefficient.